The majority of malignant tumors are currently incurable unless detected at an early stage; immunologic approaches often promise in improving therapy. The overall objective of this proposed project is to obtain new understanding of the basic mechanisms by which human major histocompatibility antigen gene expression in tumor cells is regulated by interferon. It is anticipated that such knowledge will ultimately facilitate attempts to develop more effective treatment of currently incurable cancers through cellular immune therapy and vaccine strategies. The central hypothesis of this proposal is that interferon stimulates expression of the human leukocyte antigen (HLA) Class Ia gene, HLA-A2, and the HLA Class lb gene, HLA-E, through differing and novel mechanisms. Since these two HLA Class I genes play critical roles in both cytotoxic T-cell and natural killer cell lymphocyte mediated tumor cell killing, understanding their selective regulation should increase basic knowledge about tumor immunology. The major specific aims of this proposal are (1) to determine the mechanism by which interferon-gamma mediates post-transcriptional stimulation of the HLA-A2 gene through a 3' interferon response element, and (2) to characterize the distinct interferon-gamma transcriptional response elements in the HLA-E gene promoter. To achieve these specific aims, a sequential set of molecular biological gene transfer and in vitro mutagenesis assays will be carried out to define the exact DNA and RNA sequences required for the differing regulation of these two genes in tumor cell lines and fresh leukemia cells. Cell and molecular biological assays, including confocal microscopy and in vitro RNA splicing analysis, will be carried out to define the novel mechanism of post-transcriptional regulation of the HLA-A2 gene. Biochemical methods then will be utilized to identify, characterize and purify the putative protein factors that mediate the interferon response of the HLA-A2 and HLA-E genes. Following the identification of the cis-acting DNA sequences and trans-acting factors that mediate the transcriptional response of the HLA-E gene, biochemical and genetic studies will be carried out to define protein-protein interactions and the signal transduction events that mediate the interferon response. The knowledge gained from this project will increase the basic understanding of how the HLA Class Ia and Class lb genes are differentially regulated in tumor cells, and may ultimately lead to new therapeutic approaches to optimize immunotherapy of cancer as well as allogeneic bone marrow transplantation across histocompatibility antigen barriers.